While it is nice to have both online file storage and file synchronization in the same place, it isn't a compelling reason to move for someone who already has such systems in place. However, if you don't have these kinds of systems in place already, Live Mesh is just as good as any of the other options, though I can't say it is really any better either.
Live Mesh runs as a system tray icon and it comes on at startup. Live Mesh runs two processes constantly in order to function. The Mesh Operating Environment (Moe.exe) takes nearly 44MB of RAM on my PC and the MOE Monitor (MoeMonitor.exe) chews up another 16.5MB, so all in, Live Mesh costs you 60MB of RAM. That seems pretty hefty for what it does, especially if you won't be heavily using the synchronization functionality.
For now, I'd have to say that Live Mesh is a novelty item and not a necessary addition to the user's toolkit. If mobile device support comes online, that might change things.